1. Field of the Invention
The present invention relates to a wireless power supply apparatus that supplies electric power from outside a subject to a capsule-type medical device that has been introduced into the subject, a power transmission coil unit of the wireless power supply apparatus, and a wireless power supply system that includes the capsule-type medical device and the wireless power supply apparatus.
2. Description of the Related Art
Recently, a capsule-type endoscope (hereunder, also referred to simply as “endoscope”) that includes an image pickup function and a wireless function has appeared in the field of endoscopes. The capsule-type endoscope has a configuration such that, after being swallowed by an individual to be examined that is a subject for observation (examination), the endoscope travels through the inside of internal organs such as the stomach and small intestine following the peristaltic movement thereof until being naturally excreted from the body of the individual to be examined. While the endoscope travels through the inside of the internal organs, the endoscope sequentially picks up images of the inside of the internal organs using the image pickup function.
Further, image data that is picked up inside the individual to be examined by the endoscope while traveling through the internal organs is sequentially transmitted to an external apparatus that is provided outside the individual to be examined by means of a wireless function such as wireless communication and stored in a memory. Because the individual to be examined can carry the external apparatus including the wireless function and the memory function, the individual can carry out daily activities without any inconvenience during the observation period from the time of swallowing the endoscope until excretion thereof. After the observation by the endoscope ends, a physician can display images of the internal organs on a displaying section such as a display and make a diagnosis on the basis of image data that is stored in the memory of the external apparatus.
A system that supplies electric power to a capsule-type endoscope is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2001-231186. According to the aforementioned system, since a radio capsule (corresponds to a capsule-type endoscope) is kept inside an individual to be examined, electric power is supplied to the inside of the endoscope by transmitting power to inside the endoscope from the outside of the individual to be examined. According to this system, a power transmission coil that is a power transmitting antenna is provided in an external apparatus and a power receiving coil that is a power receiving antenna is provided inside the endoscope. The external apparatus supplies power into the endoscope through the transmitting antenna and the receiving antenna to thereby enable observation operations of the capsule-type endoscope that is kept for an extended period of time inside the individual to be examined.
Further, Japanese Patent Application Laid-Open Publication No. 2004-159456 discloses an energy supply apparatus that is equipped with a plurality of power transmission coils that are disposed so as to generate a magnetic field parallel to each axis (X-axis, Y-axis, and Z-axis) of a three-dimensional orthogonal coordinate system surrounding an individual to be examined, and a power supply apparatus that supplies an electric current that changes in predetermined cycles to the plurality of power transmission coils. The aforementioned energy supply apparatus also has an energy supply amount detection section that detects an amount of energy being supplied to the plurality of power transmission coils, respectively; a detection section that detects a power transmission coil to which a supplied amount of energy is greatest among the plurality of power transmission coils based on a detection result of the energy supply amount detection section; and a selective voltage supply control section that cuts off a voltage supply to a power transmission coil other than the power transmission coil that is detected by the detection section.
According to the configuration of the energy supply apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 2004-159456, the orientations of magnetic fields emitted from power transmission coils are parallel to the respective axes of the three-dimensional orthogonal coordinate system surrounding the individual to be examined. Therefore, for example, if an axial direction of a capsule-type endoscope approximately matches any one of the axial directions of the three-dimensional orthogonal coordinate system that surrounds the individual to be examined, there is a relative increase in the power supply efficiency. In contrast, if, for example, the endoscope is oriented in a direction that corresponds to the middle between each of the axial directions of the three-dimensional orthogonal coordinate system surrounding the individual to be examined, the necessity arises to increase the intensity of a magnetic field emitted from the power transmission coil that is detected by the detection section so that power that is necessary for operations of each section of the endoscope is supplied. As a result, there is a relative decrease in the power supply efficiency.
Consequently, Japanese Patent No. 4089778 discloses a method that detects a degree of coupling between a power receiving coil and a power transmission coil, and drives a power transmission coil that is in a direction in which the degree of coupling is strong.
In this connection, Japanese Patent Application Laid-Open Publication No. 2007-175448 discloses an endoscope that observes a desired observation site by causing a capsule-type endoscope to float in a liquid inside the stomach of an individual to be examined
Further, Japanese Patent Application Laid-Open Publication No. 2005-304638 discloses technology that detects a position and an orientation of an endoscope using an exciting coil array for generating a magnetic field from a resonance circuit provided in the endoscope, and a detection coil that detects a magnetic field.